The present invention relates to a system of accurately punching holes in a fast-moving web of thermoplastic film material, and more particularly, punching holes into the web at predetermined locations through the use of a tumbling hole tube punch which plunges straight through the film into a hole in a backup roll.
In the production of various types of articles which are basically formed from a thermoplastic film material, such as polyethylene film or the like; for instance, articles such as plastic bags employed in supermarkets or plastic garbage disposal or trash bags, it is frequently necessary to provide holes in a web of the thermoplastic film material employed for the high-speed series production of the bags, which must be punched through at a high degree of accuracy with respect to the location of the holes in the film web and repetitions in successive hole patterns. Thus, for instance, with regard to plastic bags onto which tapes are to be applied, and which are used for closing trash bags in the manner of a draw string, and into which there must be provided holes in order to afford a consumer access to the tape for closing the bags, the inability of presently employed production equipment in providing accurately positioned and dimensioned holes necessitates wider border edges to be formed in the film web for the receipt of such tapes, with the result of requiring greater amounts of p1astic material in the formation of the bags thereby rendering current manufacturing methods less than optionally economical.
The apparatus and method disclosed in my aforesaid related application Ser. No. 798,518, incorporated herein by reference thereto, has overcome the foregoing problems to a substantial degree however it has left something to be desired. In my aforesaid related patent application there is described a serrated punch attached rigidly to an arm, with the arm geared to a backup roll so that the punch remains in register with the hole in the roll. Where the punch is rigidly attached to the arm, the punch enters the roll in the backup roll at an angle, so that the hole in the film is jagged in shape because of the teeth on the serrated punch. Also, the punch cuts through one edge of the hole first, allowing the chip to fall into the hole in the roll so that the film is not fully backed up during the entire punching operation. For best operation with a serrated punch, the punch should enter straight through the film so that it does not attempt to drag the film sideways. The present invention provides for the cutting teeth of the punch to enter through the film simultaneously so that the punch does enter straight.
It is an object of the present invention to provide a method and apparatus for punching a hole in a fast-moving web of film at predetermined repeat lengths at film speeds in the order of 300 ft/min. and when the diameter of the hole is as large as 2 inches in diameter.